CA2057177C - Feedback control system for the impedance control of an electric arc furnace - Google Patents
Feedback control system for the impedance control of an electric arc furnaceInfo
- Publication number
- CA2057177C CA2057177C CA002057177A CA2057177A CA2057177C CA 2057177 C CA2057177 C CA 2057177C CA 002057177 A CA002057177 A CA 002057177A CA 2057177 A CA2057177 A CA 2057177A CA 2057177 C CA2057177 C CA 2057177C
- Authority
- CA
- Canada
- Prior art keywords
- controller
- gain
- electrode
- impedance
- controlled
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
- F27B3/08—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces heated electrically, with or without any other source of heat
- F27B3/085—Arc furnaces
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D19/00—Arrangements of controlling devices
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B7/00—Heating by electric discharge
- H05B7/02—Details
- H05B7/144—Power supplies specially adapted for heating by electric discharge; Automatic control of power, e.g. by positioning of electrodes
- H05B7/148—Automatic control of power
- H05B7/156—Automatic control of power by hydraulic or pneumatic means for positioning of electrodes
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D1/00—Casings; Linings; Walls; Roofs
- F27D2001/0059—Construction elements of a furnace
- F27D2001/0066—Movable or removable parts
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D19/00—Arrangements of controlling devices
- F27D2019/0028—Regulation
- F27D2019/0034—Regulation through control of a heating quantity such as fuel, oxidant or intensity of current
- F27D2019/0037—Quantity of electric current
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D99/00—Subject matter not provided for in other groups of this subclass
- F27D99/0001—Heating elements or systems
- F27D99/0006—Electric heating elements or system
- F27D2099/0021—Arc heating
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Plasma & Fusion (AREA)
- Discharge Heating (AREA)
- Vertical, Hearth, Or Arc Furnaces (AREA)
- Furnace Details (AREA)
- Types And Forms Of Lifts (AREA)
- Elevator Control (AREA)
- Feedback Control In General (AREA)
Abstract
A feedback control system for the impedance con-trol of an electric arc furnace comprises at least one elec-trode, a hydraulic electrode actuator for adjusting the elec-trode, which actuator is adapted to be supplied with hydraulic fluid through a control valve, a controller, which is connec-ted to the valve actuator for the control valve, and impedance signal generator for delivering impedance signals to one input of said controller and a setpoint signal generator for deliver-ing a setpoint signal representing a desired impedance to an-other input of said controller. In order to prevent non-per-missible electrode oscillations in such a feedback control sy-stem it is proposed to provide a correcting stage for correcting the controller gain and to provide a correcting signal genera-tor for delivering to said correcting stage a signal which re-presents the controlled-system gain and which causes said cor-recting stage to change the controller gain in a sense which is opposite to a detected change of the controlled-system gain.
Description
FEEDBACK CONTROL SYSTEM FOR THE IMPEDANCE CONTROL OF AN
ELECTRIC ARC FURNACE
BACKGROUND OF THE INVENTION
1. Field of the Invention This invention relates to a feedback control system for the impedance control of an electric arc furnace, whlch system comprises at least one electrode, a hydraullc electrode actuator for ad~usting the electrode, whlch actuator is adapted to be supplied with hydraulic fluid through a control valve, an impedance signal generator for delivering impedance signals to one input of said controller, a setpoint signal generator for delivering a setpoint signal representing a desired impedance to another input of said controller, and a correcting stage for correcting the controller gain of said controller.
ELECTRIC ARC FURNACE
BACKGROUND OF THE INVENTION
1. Field of the Invention This invention relates to a feedback control system for the impedance control of an electric arc furnace, whlch system comprises at least one electrode, a hydraullc electrode actuator for ad~usting the electrode, whlch actuator is adapted to be supplied with hydraulic fluid through a control valve, an impedance signal generator for delivering impedance signals to one input of said controller, a setpoint signal generator for delivering a setpoint signal representing a desired impedance to another input of said controller, and a correcting stage for correcting the controller gain of said controller.
2. Description of the Prior Art In an electric arc furnace which is connected to a transformer the phase voltages and phase currents whlch are available on the secondary side of the transformer vary with the length of the electric arc or arc gap between a furnace electrode and the molten or meltable material in the furnace.
As the ratio of sald voltages and currents depends on the actual lmpedance, sald impedance may be used as a controlled variable for a control of the length of the electric arc or arc gap by means of an electrode actuator for ad~usting the ~ *
X 23224-271 ,~
- 2 _ 2057 1 77 electrode. For thls purpose lt ls known from German Patent Speclflcatlon 29 48 787 to calculate the actual impedance from the actual values of the measured phase voltages and phase currents and to compare the actual impedance with a predetermined deslred lmpedance and ln case of a devlatlon conslsting of a difference between the desired and actual impedances to control the electrode actuator for the associated electrode by means of a corresponding manipulated varlable dellvered by a controller so that the devlatlon wlll be ellmlnated. In that case, electrlcal and mechanlcal osclllatlons may be exclted ln the electrode, whlch ls held ln a carrylng arm, and the electrodes may be mechanlcally overloaded lf such osclllatlons are exclted at or near a resonant frequency of the osclllatable system conslstlng of the electrode and lts carrylng arm.
In an effort to ensure that osclllatlons of the electrodes and the assoclated carrying arms which are due to current fluctuations will be reduced to a permissable value, lt has been proposed ln Published German Applicatlon 28 41 857 to reduce the controller galn ln dependence on the magnltude of any osclllatlons whlch may occur ln the controlled varlable, l.e., ln the lmpedance whlch ls calculated from the phase voltage and phase current, so that the substantlally reduced controller galn wlll damp any osclllatlons of the controlled varlable before they can affect the manlpulated varlable. But even that measure wlll not rellably prevent an occurrence of non-permlsslble electrode osclllations, Y :;t ~, ~
~ 3 -2957177 particularly under different operatlng conditions.
SUMMARY OF THE INVENTION
It is an ob~ect of the invention to provide for the impedance control of an electric arc furnace a feedback control system which is of the kind described first hereinbefore and ls provided with comparatlvely slmple means whlch will ensure that non-permissable electrode oscillations will reliably be suppressed even under different operating conditlons.
That ob~ect ls accompllshed ln accordance with the inventlon in that the stage for correctlng the controller gain is operable to change the controller gain in a sense which is opposite to a change of the controlled-system gain under the control of a correcting signal generator delivering a signal representing the controlled-system gain.
The invention is based on the recognition that the dynamlc response of the feedback control system wlll be influenced by the dependence of the impedance on the arc length and that said dependence is nonlinear so that the dynamic response of the feedback control system cannot be independent from the instantaneous arc length, i.e., from the instantaneous operating polnt, unless the controller galn ls corrected in dependence on the instantaneous controlled-system gain, which is determined by the ratio of the impedance change to the change of the arc length and owing to the nonlinear dependence of the impedance on the arc length the controlled-2~5~1 7~
- 3a -system galn wlll change ln dependence on the arc length. For thls reason a control by whlch the overall galn of the feedback control system ls kept at least approxlmately constant wlll preclude fluctuations in the range of the dynamic response of the feedback control system so that osclllatlons resultlng from such fluctuatlons wlll be suppressed. For that purpose the controlled-system galn ls calculated ln accordance wlth known formulas from the impedance ln conslderatlon of the electrlc reslstances of the leads and the controlled-system galn thus calculated is used to control the controller galn by means of a correctlng stage ln such a manner that the overall galn of the feedback control system wlll be kept constant. If lt can be assumed that the relationshlp between the lmpedance and the arc length ls substantlally llnear close to the selected operating point, as wlll usually be the case, the correcting slgnal generator for dellverlng a slgnal representing the controlled-system gain wlll not require a slgnal representlng the actual lmpedance, provlded that the lmpedance ls automatlcally controlled, and ln that case the currently deslred lmpedance can be used ln the calculatlon of the controlled-system galn.
Particularly desirable conditions as regards the suppression of oscillations can be obtained if a further feature is adopted, which resides in that the controller is connected to a pickup for delivering a signal derived from the hydraulic pressure oscillations of the hydraulic pressure in the electrode actuator as a disturbance variable to the controller: By that disturbance feedforward, any oscillations occurring in the hydraulic electrode actuator can be eliminated by a control on a short path because such oscillations will be reflected in the hydraulic pressure applied to the electrode actuator and can be used for a compensating control of the valve for controlling the pressure applied to the electrode actuator. In that connection it must be borne in mind that the natural frequencies of the oscillatable system consisting of the electrode and the carrying arm are low frequencies. For this reason it is recommendable to provide in association with the pickup for the hydraulic pressure oscillations an oscillation filter that is tuned to the natural frequency of the electrode held in a carrying arm so that pressure oscillations near said natural frequencies will preferentially be corrected.
The invention may be summarized as a feedback control system having a controlled system gain for controlling the impedance of an electric arc furnace containing material to be melted comprising: at least one electrode having a free end located within the electric arc furnace, wherein the distance from said free end of said at least one electrode to the material defines an arc gap; a hydraulic electrode actuator coupled to said at least one electrode and including a supply of hydraulic fluid for adjusting the position of said at least one electrode to change the arc gap; a control valve coupled to said hydraulic electrode actuator for controlling the supply of hydraulic fluid;
a valve actuator coupled to said control valve for controlling said control valve; a controller coupled to said valve actuator and including a correcting stage, a difference-forming stage having a first and second inputs and a final stage to provide a corrected controller gain for controlling said valve actuator; an actual impedance signal generator coupled to said first input for transmitting a signal representing an actual impedance of the feedback control system to said controller; a set point signal generator coupled to said second input for transmitting a signal representing a desired impedance value to said controller, said controller comparing the actual impedance to the deæired impedance to calculate said controlled controller gain; and a correcting signal generator coupled to said correcting stage for transmitting a correction signal representing the controlled system gain, wherein said correcting stage adjusts said controlled controller gain in inverse proportion to said controlled ~ystem gain to calculate the corrected controller gain, whereby fluctuations in dynamic responses of the feedback control system are suppressed.
BRIEF DESCRIPTION OF THE DRAWING
-An illustrative embodiment of the invention is represented in the drawing, which is a schematic block circuit diagram illustrating a feedback control system in accordance with the invention for the impedance control of an electric arc furnace.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the drawing, the usually three-phase power supply of the electric arc furnace 1 is represented in a simplified form only as a single-phase circuit comprising only a single electrode 2, 4a whlch deflnes an arc gap wlth the molten or meltable materlal ln the furnace 1 and ls connected by an electrlc lead 3 to the secondary slde of a transformer 4 and can be vertlcally ad~usted by a hydraullc electrode actuator 5. That electrode actuator 5 conslsts ln the usual manner of a hydraullc cyllnder, whlch acts on a carrylng arm 6, by whlch the electrode 2 ls carrled. Hydraullc fluld under pressure ls supplled to the cyllnder 5 through a control valve 7, whlch ls lncluded ln a llne 8 for supplylng hydraullc fluld to the cyllnder 5. The valve actuator 9 for that control valve 7 ls controlled by a controller 10 ln dependence on the actual lmpedance of the electrlc circult whlch includes the electrode 2 and the associated arc gap. For that purpose the phase voltage and the phase current on the secondary side of the transformer 4 are detected by a voltage transformer 11 and a current transformer 12, the outputs of whlch are delivered to an impedance signal generator 13, in whlch the actual value of the lmpedance ls calculated by a division of the actual values of the phase voltage and the phase current. The calculated actual impedance is compared in a dlfference-forming stage 14 of the controller 10 wlth deslred lmpedance, whlch is represented by a slgnal delivered to the stage 14 frorn a setpoint generator 15, and the deviation whlch ls used to determine the manipulated variable ls thus calculated. But ln contrast to conventlonal controllers the devlatlon ls not used as such for a compensatlon of the devlatlon of the controlled varlable but ls dellvered to a correctlng stage 16, ln which ~ 23224-271 X ''}~
the slgnal representlng the deviation is corrected ln dependence on the controlled-system galn so as to maintain the overall gain of the feedback control system constant. For that purpose the correcting stage is connected to a correcting signal generator 17 for generating a signal representing the controlled-system gain, which in the embodiment shown by way of example is calculated from the actual lmpedance wlth an allowance for the reslstance and lnductive reactance of the electric lead 3. Slgnals representing the actual impedance are delivered to the correcting signal generator 17 from the impedance signal generator 13 via a branch line 18. The values of the resistance and reactance are measured or calculated and will depend on the existlng leads and may be considered constant, and correspondlng signals are delivered to the correcting signal generator 17 via corresponding inputs 19 .
Because the controlled-system gain depends on the ratio of the impedance to the arc length and the dependence of the impedance on the arc length ls nonllnear, the use of a controller havlng a constant controller galn would have the result that a change of the arc length caused, e.g., by a change of the operatlng conditions would result also in a change of the dynamic control response of the feedback control system although such a change should desirably be avoided.
For this reason the controller galn ls changed ln a sense whlch is opposite to the sense in which the controlled-system gain is changed so that the overall gain corresponding to the .~
product of the controller galn and controlled-system galn wlll remaln constant and, as a result, the dynamlc control response wlll be constant too. In the embodlment shown by way of example the correctlng stage 16 for controlllng the controller galn influences the slgnal whlch represents the devlatlon.
But that ls not the only way ln which a correctlon can be effected because the controller galn may alternatlvely be changed by an lnfluence on the actual lmpedance slgnal or on the manipulated varlable.
In dependence on the corrected lnput signal fed to the flnal stage 20 of the controller 10 the manlpulated varlable appearlng at the output of the controller stage 20 wlll match the lnstantaneous operatlng polnt and wlll ensure that the automatic control of the electrode in dependence on the lmpedance wlll not glve rlse to osclllatlons near that operating point.
For a direct ellmlnatlon of osclllatlons occurring ad~acent to the electrode actuator 5, hydraullc pressure oscillatlons occurring ad~acent to the hydraulic cylinder 6 are detected by a plckup 21, whlch dellvers a corresponding disturbance variable to the controller stage 20 so that a control that opposes the pressure osclllatlons can be effected on a short path by a suitable lnfluence on the manipulated variable for controlling the control valve 7. The pickup 21 for the hydraullc pressure osclllatlons comprises a pressure gage 22, whlch ls connected in a series with a dlfference-formlng stage 23 so that only the osclllations of the pressure X ; 23224-271 - 7a - 20571 77 wlll be detected. An osclllation filter 24 may be associated for a preferential response to the pressure fluctuations near the natural frequencies of the oscillatable system consisting of the electrode 2 and the carrying arm 6.
It will be understood that the invention is not restricted to the embodiment shown by way of example. For instance, the correcting signal generator 17 for indicating the controlled-system gain may be connected on its input side to the setpoint signal generator 15 rather than to the impedance signal generator 13 so that the controller galn will be changed only by a change of the setpoint in dependence on a desired change of the operating point. That mode of operation can readily be adopted if the impedance is properly controlled because a linear response can be expected near an operating point.
As the ratio of sald voltages and currents depends on the actual lmpedance, sald impedance may be used as a controlled variable for a control of the length of the electric arc or arc gap by means of an electrode actuator for ad~usting the ~ *
X 23224-271 ,~
- 2 _ 2057 1 77 electrode. For thls purpose lt ls known from German Patent Speclflcatlon 29 48 787 to calculate the actual impedance from the actual values of the measured phase voltages and phase currents and to compare the actual impedance with a predetermined deslred lmpedance and ln case of a devlatlon conslsting of a difference between the desired and actual impedances to control the electrode actuator for the associated electrode by means of a corresponding manipulated varlable dellvered by a controller so that the devlatlon wlll be ellmlnated. In that case, electrlcal and mechanlcal osclllatlons may be exclted ln the electrode, whlch ls held ln a carrylng arm, and the electrodes may be mechanlcally overloaded lf such osclllatlons are exclted at or near a resonant frequency of the osclllatable system conslstlng of the electrode and lts carrylng arm.
In an effort to ensure that osclllatlons of the electrodes and the assoclated carrying arms which are due to current fluctuations will be reduced to a permissable value, lt has been proposed ln Published German Applicatlon 28 41 857 to reduce the controller galn ln dependence on the magnltude of any osclllatlons whlch may occur ln the controlled varlable, l.e., ln the lmpedance whlch ls calculated from the phase voltage and phase current, so that the substantlally reduced controller galn wlll damp any osclllatlons of the controlled varlable before they can affect the manlpulated varlable. But even that measure wlll not rellably prevent an occurrence of non-permlsslble electrode osclllations, Y :;t ~, ~
~ 3 -2957177 particularly under different operatlng conditions.
SUMMARY OF THE INVENTION
It is an ob~ect of the invention to provide for the impedance control of an electric arc furnace a feedback control system which is of the kind described first hereinbefore and ls provided with comparatlvely slmple means whlch will ensure that non-permissable electrode oscillations will reliably be suppressed even under different operating conditlons.
That ob~ect ls accompllshed ln accordance with the inventlon in that the stage for correctlng the controller gain is operable to change the controller gain in a sense which is opposite to a change of the controlled-system gain under the control of a correcting signal generator delivering a signal representing the controlled-system gain.
The invention is based on the recognition that the dynamlc response of the feedback control system wlll be influenced by the dependence of the impedance on the arc length and that said dependence is nonlinear so that the dynamic response of the feedback control system cannot be independent from the instantaneous arc length, i.e., from the instantaneous operating polnt, unless the controller galn ls corrected in dependence on the instantaneous controlled-system gain, which is determined by the ratio of the impedance change to the change of the arc length and owing to the nonlinear dependence of the impedance on the arc length the controlled-2~5~1 7~
- 3a -system galn wlll change ln dependence on the arc length. For thls reason a control by whlch the overall galn of the feedback control system ls kept at least approxlmately constant wlll preclude fluctuations in the range of the dynamic response of the feedback control system so that osclllatlons resultlng from such fluctuatlons wlll be suppressed. For that purpose the controlled-system galn ls calculated ln accordance wlth known formulas from the impedance ln conslderatlon of the electrlc reslstances of the leads and the controlled-system galn thus calculated is used to control the controller galn by means of a correctlng stage ln such a manner that the overall galn of the feedback control system wlll be kept constant. If lt can be assumed that the relationshlp between the lmpedance and the arc length ls substantlally llnear close to the selected operating point, as wlll usually be the case, the correcting slgnal generator for dellverlng a slgnal representing the controlled-system gain wlll not require a slgnal representlng the actual lmpedance, provlded that the lmpedance ls automatlcally controlled, and ln that case the currently deslred lmpedance can be used ln the calculatlon of the controlled-system galn.
Particularly desirable conditions as regards the suppression of oscillations can be obtained if a further feature is adopted, which resides in that the controller is connected to a pickup for delivering a signal derived from the hydraulic pressure oscillations of the hydraulic pressure in the electrode actuator as a disturbance variable to the controller: By that disturbance feedforward, any oscillations occurring in the hydraulic electrode actuator can be eliminated by a control on a short path because such oscillations will be reflected in the hydraulic pressure applied to the electrode actuator and can be used for a compensating control of the valve for controlling the pressure applied to the electrode actuator. In that connection it must be borne in mind that the natural frequencies of the oscillatable system consisting of the electrode and the carrying arm are low frequencies. For this reason it is recommendable to provide in association with the pickup for the hydraulic pressure oscillations an oscillation filter that is tuned to the natural frequency of the electrode held in a carrying arm so that pressure oscillations near said natural frequencies will preferentially be corrected.
The invention may be summarized as a feedback control system having a controlled system gain for controlling the impedance of an electric arc furnace containing material to be melted comprising: at least one electrode having a free end located within the electric arc furnace, wherein the distance from said free end of said at least one electrode to the material defines an arc gap; a hydraulic electrode actuator coupled to said at least one electrode and including a supply of hydraulic fluid for adjusting the position of said at least one electrode to change the arc gap; a control valve coupled to said hydraulic electrode actuator for controlling the supply of hydraulic fluid;
a valve actuator coupled to said control valve for controlling said control valve; a controller coupled to said valve actuator and including a correcting stage, a difference-forming stage having a first and second inputs and a final stage to provide a corrected controller gain for controlling said valve actuator; an actual impedance signal generator coupled to said first input for transmitting a signal representing an actual impedance of the feedback control system to said controller; a set point signal generator coupled to said second input for transmitting a signal representing a desired impedance value to said controller, said controller comparing the actual impedance to the deæired impedance to calculate said controlled controller gain; and a correcting signal generator coupled to said correcting stage for transmitting a correction signal representing the controlled system gain, wherein said correcting stage adjusts said controlled controller gain in inverse proportion to said controlled ~ystem gain to calculate the corrected controller gain, whereby fluctuations in dynamic responses of the feedback control system are suppressed.
BRIEF DESCRIPTION OF THE DRAWING
-An illustrative embodiment of the invention is represented in the drawing, which is a schematic block circuit diagram illustrating a feedback control system in accordance with the invention for the impedance control of an electric arc furnace.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the drawing, the usually three-phase power supply of the electric arc furnace 1 is represented in a simplified form only as a single-phase circuit comprising only a single electrode 2, 4a whlch deflnes an arc gap wlth the molten or meltable materlal ln the furnace 1 and ls connected by an electrlc lead 3 to the secondary slde of a transformer 4 and can be vertlcally ad~usted by a hydraullc electrode actuator 5. That electrode actuator 5 conslsts ln the usual manner of a hydraullc cyllnder, whlch acts on a carrylng arm 6, by whlch the electrode 2 ls carrled. Hydraullc fluld under pressure ls supplled to the cyllnder 5 through a control valve 7, whlch ls lncluded ln a llne 8 for supplylng hydraullc fluld to the cyllnder 5. The valve actuator 9 for that control valve 7 ls controlled by a controller 10 ln dependence on the actual lmpedance of the electrlc circult whlch includes the electrode 2 and the associated arc gap. For that purpose the phase voltage and the phase current on the secondary side of the transformer 4 are detected by a voltage transformer 11 and a current transformer 12, the outputs of whlch are delivered to an impedance signal generator 13, in whlch the actual value of the lmpedance ls calculated by a division of the actual values of the phase voltage and the phase current. The calculated actual impedance is compared in a dlfference-forming stage 14 of the controller 10 wlth deslred lmpedance, whlch is represented by a slgnal delivered to the stage 14 frorn a setpoint generator 15, and the deviation whlch ls used to determine the manipulated variable ls thus calculated. But ln contrast to conventlonal controllers the devlatlon ls not used as such for a compensatlon of the devlatlon of the controlled varlable but ls dellvered to a correctlng stage 16, ln which ~ 23224-271 X ''}~
the slgnal representlng the deviation is corrected ln dependence on the controlled-system galn so as to maintain the overall gain of the feedback control system constant. For that purpose the correcting stage is connected to a correcting signal generator 17 for generating a signal representing the controlled-system gain, which in the embodiment shown by way of example is calculated from the actual lmpedance wlth an allowance for the reslstance and lnductive reactance of the electric lead 3. Slgnals representing the actual impedance are delivered to the correcting signal generator 17 from the impedance signal generator 13 via a branch line 18. The values of the resistance and reactance are measured or calculated and will depend on the existlng leads and may be considered constant, and correspondlng signals are delivered to the correcting signal generator 17 via corresponding inputs 19 .
Because the controlled-system gain depends on the ratio of the impedance to the arc length and the dependence of the impedance on the arc length ls nonllnear, the use of a controller havlng a constant controller galn would have the result that a change of the arc length caused, e.g., by a change of the operatlng conditions would result also in a change of the dynamic control response of the feedback control system although such a change should desirably be avoided.
For this reason the controller galn ls changed ln a sense whlch is opposite to the sense in which the controlled-system gain is changed so that the overall gain corresponding to the .~
product of the controller galn and controlled-system galn wlll remaln constant and, as a result, the dynamlc control response wlll be constant too. In the embodlment shown by way of example the correctlng stage 16 for controlllng the controller galn influences the slgnal whlch represents the devlatlon.
But that ls not the only way ln which a correctlon can be effected because the controller galn may alternatlvely be changed by an lnfluence on the actual lmpedance slgnal or on the manipulated varlable.
In dependence on the corrected lnput signal fed to the flnal stage 20 of the controller 10 the manlpulated varlable appearlng at the output of the controller stage 20 wlll match the lnstantaneous operatlng polnt and wlll ensure that the automatic control of the electrode in dependence on the lmpedance wlll not glve rlse to osclllatlons near that operating point.
For a direct ellmlnatlon of osclllatlons occurring ad~acent to the electrode actuator 5, hydraullc pressure oscillatlons occurring ad~acent to the hydraulic cylinder 6 are detected by a plckup 21, whlch dellvers a corresponding disturbance variable to the controller stage 20 so that a control that opposes the pressure osclllatlons can be effected on a short path by a suitable lnfluence on the manipulated variable for controlling the control valve 7. The pickup 21 for the hydraullc pressure osclllatlons comprises a pressure gage 22, whlch ls connected in a series with a dlfference-formlng stage 23 so that only the osclllations of the pressure X ; 23224-271 - 7a - 20571 77 wlll be detected. An osclllation filter 24 may be associated for a preferential response to the pressure fluctuations near the natural frequencies of the oscillatable system consisting of the electrode 2 and the carrying arm 6.
It will be understood that the invention is not restricted to the embodiment shown by way of example. For instance, the correcting signal generator 17 for indicating the controlled-system gain may be connected on its input side to the setpoint signal generator 15 rather than to the impedance signal generator 13 so that the controller galn will be changed only by a change of the setpoint in dependence on a desired change of the operating point. That mode of operation can readily be adopted if the impedance is properly controlled because a linear response can be expected near an operating point.
Claims (4)
1. A feedback control system having a controlled system gain for controlling the impedance of an electric arc furnace containing material to be melted comprising: at least one electrode having a free end located within the electric arc furnace, wherein the distance from said free end of said at least one electrode to the material defines an arc gap; a hydraulic electrode actuator coupled to said at least one electrode and including a supply of hydraulic fluid for adjusting the position of said at least one electrode to change the arc gap; a control valve coupled to said hydraulic electrode actuator for controlling the supply of hydraulic fluid; a valve actuator coupled to said control valve for controlling said control valve; a controller coupled to said valve actuator and including a correcting stage, a difference-forming stage having a first and second inputs and a final stage to provide a corrected controller gain for controlling said valve actuator; an actual impedance signal generator coupled to said first input for transmitting a signal representing an actual impedance of the feedback control system to said controller; a set point signal generator coupled to said second input for transmitting a signal representing a desired impedance value to said controller, said controller comparing the actual impedance to the desired impedance to calculate said controlled controller gain; and a correcting signal generator coupled to said correcting stage for transmitting a correction signal representing the controlled system gain, wherein said correcting stage adjusts said controlled controller gain in inverse proportion to said controlled system gain to calculate the corrected controller gain, whereby fluctuations in dynamic responses of the feedback control system are suppressed.
2. A feedback control system according to claim 1, additionally including a pick-up for detecting hydraulic pressure oscillations in said valve actuator, said pick-up being coupled to said controller for transmitting a signal to said controller representative of a disturbance variable derived from the pressure oscillations.
3. A feedback control system according to claim 2, additionally including a carrying arm coupled to said at least one electrode, said at least one electrode and said carrying arm defining an oscillation system having a fundamental frequency, and an oscillation filter, tuned to said fundamental frequency, coupled between said pick-up and said controller for detecting the hydraulic pressure oscillations.
4. A feedback control system according to claim 1, additionally including an overall gain defined by the product of the controlled controller gain and the controlled system gain, wherein said correcting stage adjusts the controller gain to maintain a constant overall gain.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ATA2477/90 | 1990-12-07 | ||
| AT0247790A AT395657B (en) | 1990-12-07 | 1990-12-07 | CONTROL CIRCUIT FOR IMPEDANCE CONTROL OF AN ARC FURNACE |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2057177A1 CA2057177A1 (en) | 1992-06-08 |
| CA2057177C true CA2057177C (en) | 1996-05-28 |
Family
ID=3535048
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002057177A Expired - Fee Related CA2057177C (en) | 1990-12-07 | 1991-12-06 | Feedback control system for the impedance control of an electric arc furnace |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US5255285A (en) |
| EP (1) | EP0490869B1 (en) |
| JP (1) | JPH04308686A (en) |
| AT (1) | AT395657B (en) |
| CA (1) | CA2057177C (en) |
| DE (1) | DE59102012D1 (en) |
| ES (1) | ES2055983T3 (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6411643B1 (en) * | 1999-09-30 | 2002-06-25 | Sms Demag, Inc | Automatic electrode regulator based on direct power factor regulation and method |
| US6603795B2 (en) * | 2001-02-08 | 2003-08-05 | Hatch Associates Ltd. | Power control system for AC electric arc furnace |
| US6573691B2 (en) | 2001-10-17 | 2003-06-03 | Hatch Associates Ltd. | Control system and method for voltage stabilization in electric power system |
| US7295593B2 (en) | 2004-09-01 | 2007-11-13 | Hatch Ltd. | System and method of minimizing loss of electrical conduction during input of feed material to a furnace |
| GB2430276B (en) * | 2005-09-20 | 2009-09-16 | Advanced Mineral Recovery Tech | Control system for an arc furnace |
| US7313160B1 (en) * | 2005-12-14 | 2007-12-25 | Graftech International Holdings Inc. | Regulation system analysis method |
| US20080056327A1 (en) * | 2006-08-30 | 2008-03-06 | Hatch Ltd. | Method and system for predictive electrode lowering in a furnace |
| JP5742400B2 (en) * | 2011-04-07 | 2015-07-01 | 東芝三菱電機産業システム株式会社 | AC arc furnace electrode lifting device |
| US9383278B1 (en) | 2014-04-22 | 2016-07-05 | Contractors & Industrial Supply Company, Inc. | Electrode torque measurement device |
| CN104406415B (en) * | 2014-11-13 | 2016-08-24 | 攀枝花钢城集团瑞钢工业有限公司 | Electric furnace electrode regulation system |
| US9850105B1 (en) | 2015-05-04 | 2017-12-26 | Contractors & Industrial Supply Company, Inc. | Vertical automatic addition tong apparatus |
| CN106370023A (en) * | 2016-09-30 | 2017-02-01 | 湖北华宏电力科技有限公司 | Submerged arc furnace energy optimization energy saving system |
| WO2021241538A1 (en) * | 2020-05-29 | 2021-12-02 | Ｊｆｅマテリアル株式会社 | Operation method of stationary electric furnace |
| CN113959686A (en) * | 2021-09-03 | 2022-01-21 | 中国重型机械研究院股份公司 | Detection device and calibration method for electrode lifting system of LF (ladle furnace) |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2367979A (en) * | 1942-12-08 | 1945-01-23 | Westinghouse Electric & Mfg Co | Furnace regulator system |
| US2921107A (en) * | 1958-07-01 | 1960-01-12 | Mc Graw Edison Co | Control system for arc furnace |
| US3186043A (en) * | 1963-04-02 | 1965-06-01 | Allegheny Ludlum Steel | Metallurgical furnace control |
| BE758327A (en) * | 1969-10-30 | 1971-04-01 | Nippon Kokan Kk | METHOD AND SYSTEM FOR REGULATING ELECTRIC OVEN |
| US4029888A (en) * | 1976-05-27 | 1977-06-14 | Robicon Corporation | Arc furnace control system |
| US4096344A (en) * | 1976-09-30 | 1978-06-20 | Westinghouse Electric Corp. | Electric arc furnace control system |
| DE2731014C3 (en) * | 1977-07-08 | 1980-05-14 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Device for controlling a three-phase electric arc furnace |
| GB2001461B (en) * | 1977-07-21 | 1982-01-13 | Leybold Heraeus Gmbh & Co Kg | Arrangement for controlling the depth of immersion of self-consuming electrodes in electro-slag remelting furnaces |
| DE2841857B2 (en) * | 1978-09-26 | 1980-10-16 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Arrangement for regulating the impedance of an electric arc furnace by adjusting the height of the electrodes |
| DE2901198C2 (en) * | 1979-01-13 | 1988-07-28 | Mannesmann Rexroth GmbH, 8770 Lohr | Electrode control of electric arc furnaces using hydraulic lifting cylinders |
| DE2948787C2 (en) * | 1979-12-04 | 1984-05-03 | Siemens AG, 1000 Berlin und 8000 München | Arrangement for the electrode control of an electric arc furnace |
| DE3242934A1 (en) * | 1982-11-20 | 1984-05-24 | Mannesmann Rexroth GmbH, 8770 Lohr | CONTROL DEVICE FOR ADJUSTING THE ELECTRODE OF AN ARC FURNACE |
| DE3512189C2 (en) * | 1985-04-03 | 1996-09-05 | Mannesmann Ag | Method and device for controlling arc furnaces |
-
1990
- 1990-12-07 AT AT0247790A patent/AT395657B/en not_active IP Right Cessation
-
1991
- 1991-11-19 EP EP91890289A patent/EP0490869B1/en not_active Expired - Lifetime
- 1991-11-19 ES ES91890289T patent/ES2055983T3/en not_active Expired - Lifetime
- 1991-11-19 DE DE59102012T patent/DE59102012D1/en not_active Expired - Fee Related
- 1991-12-02 US US07/801,012 patent/US5255285A/en not_active Expired - Fee Related
- 1991-12-06 JP JP3322996A patent/JPH04308686A/en active Pending
- 1991-12-06 CA CA002057177A patent/CA2057177C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US5255285A (en) | 1993-10-19 |
| AT395657B (en) | 1993-02-25 |
| EP0490869A1 (en) | 1992-06-17 |
| JPH04308686A (en) | 1992-10-30 |
| ATA247790A (en) | 1992-06-15 |
| ES2055983T3 (en) | 1994-09-01 |
| EP0490869B1 (en) | 1994-06-22 |
| CA2057177A1 (en) | 1992-06-08 |
| DE59102012D1 (en) | 1994-08-04 |
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| EEER | Examination request | ||
| MKLA | Lapsed |